Laser spectroscopy of trapped atomic ions

Recent developments in laser spectroscopy of atomic ions stored in electromagnetic traps are reviewed with empha-sis on techniques that appear to hold the greatest promise of attaining extremely high resolution. Among these techniques are laser cooling and the use of single, isolated ions as experimental samples. Doppler shifts and other perturbing influences can be largely eliminated. Atomic resonances with line widths of a few parts in 10 " have been observed at frequencies ranging &om the radio frequency to the ultraviolet. Experimental accuracies of one part in lo' * appear to be attainable. TOMIC SPECTROSCOPY DATES FROM THE I V H CENTURY, when it was discovered that atomic vapors emitted and A absorbed light at discrete resonance wavelengths, character-istic of each chemical element. When the quantum theory of atoms was developed in the 20th century by Niels Bohr and others, it wa